Individual single wall carbon nanotubes (SWCNTs) have large surface area and extraordinary strength, with high electrical and thermal conductivity. Bulk, composite materials containing SWCNTs have been developed, including sheets with high electrical and thermal conductivities and fibers and foams with high mechanical strength. SWCNT forests with electron-emission properties have been utilized in display and energy storage applications. Bulk SWCNT materials have also been considered for photovoltaic devices, thermoelectric converters, and artificial muscles. Unfortunately, most macroscale materials with SWCNTs do not reflect the large surface area, strength or conductivity of individual SWCNTs.
Three dimensional (3D) porous carbon nanotube (CNT) networks or aerogels are a class of bulk CNT materials that combine high electrical conductivity of CNTs with high surface area and are thermally insulating due to low CNT density. Porous CNT networks have been fabricated by drawing multiwall CNTs (MWCNTs) from MWCNT forests. Solution-processed CNT aerogels have been formed using a mixture of SWCNTs and MWCNTs. For some applications, SWCNTs have physical properties that are superior to those of MWCNTs. However, elastic gels of only SWCNTs produced with known methodologies were significantly more fragile than MWCNT gels, due at least in part to the shorter length of SWCNTs (˜1 μm) compared to MWCNTs (tens of μm). Shorter SWCNTs have fewer entanglements; increased CNT entanglements increase gel stiffness and stability. Typically, the SWCNT elastic gels collapsed or the aerogels cracked during fabrication. Moreover, known SWCNT-based bulk materials have a specific surface area (SSA) at least an order of magnitude lower than that thought to be theoretically possible (e.g., about 1315 m2/g for SWCNTs with closed-ends and about 1600 m2/g for SWCNTs with open-ends).
CNT-based elastic conductors typically offer modest electrical conductivity, require high concentration of CNTs, are opaque, and exhibit significantly decreased electrical conductivity when stretched. Furthermore, graphene and CNTs phase-segregate or agglomerate within elastomers during dispersion, hindering practical scale usage of graphene- or CNT-based elastic conductors. The poor enhancement of mechanical properties of the composites is ascribed to the agglomeration or bundling of SWCNTs by strong van der Waals interactions.